Methane gas from decaying dog poop on the outside lawn.
Let me tell you something that happened to my husband last week in Houston. He went to check his bag in at the counter, and they waved a wand over it to check for explosives. The thing went off like crazy!!! My husband said, "Uh...what's going on?" She said, "It tested positive for
nitro..." He said, "
DO WHAT"? So, they are asking him why he was in Houston, where he was, why he has such a small bag for an 8 day trip, why he changed flights 3 times, etc. He has answers for all of these questions: 1) Working on a project in Houston. 2)I thought I was only going to be here 3-4 days...look at the dry-cleaning tags from the hotel bill. 3) Because I thought I would be
leaving each day that I made the flight arrangements. Of course, the fact that he was from FLORIDA did not help at all. But...as they are throwing out his underwear for all the world to see....he says, "Wait a minute. My sneakers are in that bag...I work in the phosphate industry in Central Florida, and I probably have fertilizer on those sneakers because that's what I wear there sometimes when I have to deliver a pump."
Bingo. That's what it was.
However, HE NEVER EVEN THOUGHT about leaving the terminal. He figured he'd be shot.